Is it possible to manually sculpt a specific face in Blender ultra-accurately?
In theory, yes, if you have enough reference material and time, it would be possible. The end result is after all basically just a mesh and some textures, independent opf the method used to create it. However it takes a lot of skill to create lifelike copies of human faces, so if you intend to learn to do this yourself, expect to put in a lot of effort and experience a lot of frustration before you get something that looks reasonably good.

Its also worth noting that 3d scans also generally need a fair bit of manual work to get the best results, for example the image you have included has a number of artifacts including the eyebrows (which should probably be replaced with particle hair for a  more realistic reproduction.